Disease in humans may be produced by several species of Ancylostoma besides Ancylostoma duodenale, the natural hookworm of man. Cutaneous and visceral larva migrans are known to be caused by the hookworms of animals, particularly certain Ancylostoma species of dogs and cats. However, the behavior of the larvae of these parasites in man and in other mammalian hosts is not completely known. The objectives in the proposed project are to study the behavior of several animal species of Ancylostoma in their natural hosts and in other mammals in order to 1) predict the behavior in man of the larvae of these and other hookworms of the genus Ancylostoma, 2) devise methods of controlling these parasites in man and in animals which serve as sources of infections for man, and 3) characterize the genus Ancylostoma in regards to the life cycle patterns and certain biological characteristics which may be common to all of its members, e.g., paratenesis, arrested larval development, and transmammary transmission. The study of the behavior of these hookworms in their natural hosts is also expected to lead a clearer understanding of the behavior of Ancylostoma duodenale in man and the nature of the disease it produces.